This invention relates to guidance systems for guidance of spacecraft to or from rendezvous.
It may often be desirable to cause one spacecraft to approach (or leave) another spacecraft from a substantial distance to a relatively close distance in order that the spacecraft may then be docked. An example of such an approach and separation might relate to refueling or repair of a low earth orbiting satellite. If fuel should be depleted or a failure should occur in a replaceable module of such a satellite, a manned space shuttle or possibly an unmanned repair vehicle might reach it. Under such circumstances, docking might occur, or it might well be that no actual docking of the space shuttle with the communications satellite would be necessary, as extra-vehicular activity (EVA) could be used to effect the fueling or repairs. The repaired satellite could then be returned to its operational orbit.
It is very desirable to use a television camera or other imaging device as the sensor for approach and docking navigation, for the camera provides information relative to target attitude as well as to overall visually determinable conditions such as improperly deployed appendages, broken pieces, intervening objects, potential collisions and the like.
When a maneuvering spacecraft and a target vehicle are in relatively close proximity, the camera can provide information regarding the distance therebetween. In particular, the distance can readily be determined by triangulation between the camera's point of observation on the observing spacecraft and two or more locations on the target vehicle which have known separations. Under such conditions, well known control systems and techniques may be used to effect docking or separation of the vehicles. Depending upon the size of the target vehicle, there will be a distance at which the apparent separation of locations on the vehicle is so small that they either cannot be separately resolved at all, or, if they can be resolved, the error in the triangulation is too large for an accurate determination of distance. At such distances, it is customary to use an auxiliary means such as radar to determine the inter-vehicle distance.
An improved medium-distance approach or separation apparatus and method is desired.